This invention relates to a separator for separating particles of different densities, by treatment of suspensions of the particles in a liquid, and concerns separation of suspensions containing material distributed over a range of density and/or particle size. The invention is especially concerned with the treatment of suspended material of very small particle size such as for example, sand tailings from mineral dressing equipment which tailings in current practice are normally discharged to waste even though they contain valuable metalliferous components. For example, sand tailings from a typical mill might range from 20 British Standard mesh to 400 mesh with small proportions even finer.
In commonly owned U.K. Pat. No. 1,174,405, there is described a gravity separator which was developed primarily to handle tin bearing slimes to recover residual tin which at that time could not be recovered with existing equipment of conventional type. Apparatus in accordance with U.K. Pat. No. 1,174,405 has been available and extensively used for some years and has given excellent performance enabling very considerable savings to be made in the tin mining and other industries. The principle of operation of the apparatus of U.K. Pat. No. 1,174,405 is that of adjusting shear conditions in a flowing suspension by applying a shaking motion of variable amplitude and frequency in order to cause the heavier material to remain on a moving surface, and form a close packed deposit or bank, while the finer particles remain in suspension and advance along the surface. The decks are freely suspended and are moved by a vibratory shaking action using an unbalanced-weight drive which, although simple and reliable, is such that the path traced out by the decks with a given weight rotating at fixed radius will undesirably vary according to the total shaken weight. In certain applications, it has also become necessary to employ lower frequencies and then, particularly when the frequency employed approaches the natural frequency of the apparatus, control problems can arise.